NAVIGATION AERONAUTICAL CHARTS

Air navigation is the process of piloting an airplane from one geographic position to another while monitoring one's position as the flight progresses. It introduces the need for planning, which includes plotting the course on an aeronautical chart, selecting checkpoints, measuring distances, obtaining pertinent weather information, and computing flight time, headings, and fuel requirements. The methods used include pilotage—navigating by reference to visible landmarks, dead reckoning—computations of direction and distance from a known position, and radio navigation—by use of radio aids.

An aeronautical chart is the road map for a pilot flying under VFR. The chart provides information which allows pilots to track their position and provides available information which enhances safety. The three aeronautical charts used by VFR pilots are:

• Sectional Charts
• VFR Terminal Area Charts
• World Aeronautical Charts

A free catalog listing aeronautical charts and related publications including prices and instructions for ordering is available at the National Aeronautical Charting Office (NACO) Web site: www.naco.faa.gov.

SECTIONAL CHARTS
Sectional charts are the most common charts used by pilots today. The charts have a scale of 1:500,000 (1 inch = 6.86 nautical miles or approximately 8 statute miles) which allows for more detailed information to be included on the chart.

The charts provide an abundance of information, including airport data, navigational aids, airspace, and topography. Figure 14-1 on the next page is an excerpt from the legend of a sectional chart. By referring to the chart legend, a pilot can interpret most of the information on the chart. A pilot should also check the chart for other legend information, which includes air traffic control frequencies and information on airspace. These charts are revised semiannually except for some areas outside the conterminous United States where they are revised annually.

VISUAL FLIGHT RULE TERMINAL AREA CHARTS
Visual flight rule (VFR) terminal area charts are helpful when flying in or near Class B airspace. They have a scale of 1:250,000 (1 inch = 3.43 nautical miles or approximately 4 statute miles). These charts provide a more detailed display of topographical information and are revised semiannually, except for several Alaskan and Caribbean charts.

WORLD AERONAUTICAL CHARTS
World aeronautical charts are designed to provide a standard series of aeronautical charts, covering land areas of the world, at a size and scale convenient for navigation by moderate speed aircraft. They are produced at a scale of 1:1,000,000 (1 inch = 13.7 nautical miles or approximately 16 statute miles). These charts are similar to sectional charts and the symbols are the same except there is less detail due to the smaller scale.

These charts are revised annually except several Alaskan charts and the Mexican/Caribbean charts which are revised every 2 years.

OTHER AIRSPACE AREAS

"Other airspace areas" is a general term referring to the majority of the remaining airspace. It includes:

• Airport Advisory Areas
• Military Training Routes (MTR)
• Temporary Flight Restrictions
• Parachute Jump Areas
• Published VFR Routes
• Terminal Radar Service Areas
• National Security Areas

AIRPORT ADVISORY AREAS
An airport advisory area is an area within 10 statute miles (SM) of an airport where a control tower is not operating, but where a flight service station (FSS) is located. At these locations, the FSS provides advisory service to arriving and departing aircraft.

MILITARY TRAINING ROUTES
Military training routes (MTR) are developed to allow the military to conduct low-altitude, highspeed training. The routes above 1,500 feet AGL are developed to be flown primarily under IFR, and the routes 1,500 feet and less are for VFR flight. The routes are identified on sectional charts by the designation "instrument (IR) or visual (VR)."

TEMPORARY FLIGHT RESTRICTIONS
An FDC NOTAM will be issued to designate a temporary flight restriction (TFR). The NOTAM will begin with the phrase "FLIGHT RESTRICTIONS" followed by the location of the temporary restriction, effective time period, area defined in statute miles, and altitudes affected. The NOTAM will also contain the FAA coordination facility and telephone number, the reason for the restriction, and any other information deemed appropriate. The pilot should check the NOTAMs as part of flight planning.

Some of the purposes for establishing a temporary restriction are:

• Protect persons and property in the air or on the surface from an existing or imminent hazard.
• Provide a safe environment for the operation of disaster relief aircraft.
• Prevent an unsafe congestion of sightseeing aircraft above an incident or event, which may generate a high degree of public interest.
• Protect declared national disasters for humanitarian reasons in the State of Hawaii.
• Protect the President, Vice President, or other public figures.
• Provide a safe environment for space agency operations.

PARACHUTE JUMP AREAS
Parachute jump areas are published in the Airport/Facility Directory. Sites that are used frequently are depicted on sectional charts.

PUBLISHED VFR ROUTES
Published VFR routes are for transitioning around, under, or through some complex airspace. Terms such as VFR flyway, VFR corridor, Class B airspace, VFR transition route, and terminal area VFR route have been applied to such routes. These routes are generally found on VFR terminal area planning charts.

TERMINAL RADAR SERVICE AREAS
Terminal Radar Service Areas (TRSA) are areas where participated pilots can receive additional radar services. The purpose of the service is to provide separation between all IFR operations and participated VFR aircraft.

The primary airport within the TRSA becomes Class D airspace. The remaining portion of the TRSA overlies other controlled airspace, which is normally Class E airspace beginning at 700 or 1,200 feet and established to transition to/from the en route terminal environment. TRSAs are depicted on VFR sectional charts and terminal area charts with a solid black line and altitudes for each segment. The Class D portion is charted with a blue segmented line.

Participation in TRSA services is voluntary; however, pilots operating under VFR are encouraged to contact the radar approach control and take advantage of TRSA service.

NATIONAL SECURITY AREAS
National security areas consist of airspace of defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities. Pilots are requested to voluntarily avoid flying through these depicted areas. When necessary, flight may be temporarily prohibited.

UNCONTROLLED AND SPECIAL USE AIRSPACE

UNCONTROLLED AIRSPACE
CLASS G AIRSPACE
Uncontrolled airspace or Class G airspace is the portion of the airspace that has not been designated as Class A, B, C, D, or E. It is therefore designated uncontrolled airspace. Class G airspace extends from the surface to the base of the overlying Class E airspace. Although air traffic control (ATC) has no authority or responsibility to control air traffic, pilots should remember there are VFR minimums which apply to Class G airspace.


SPECIAL USE AIRSPACE
Special use airspace exists where activities must be confined because of their nature. In special use airspace, limitations may be placed on aircraft that are not a part of the activities. Special use airspace usually consists of:

• Prohibited Areas
• Restricted Areas
• Warning Areas
• Military Operation Areas
• Alert Areas
• Controlled Firing Areas

PROHIBITED AREAS
Prohibited areas are established for security or other reasons associated with the national welfare. Prohibited areas are published in the Federal Register and are depicted on aeronautical charts.

RESTRICTED AREAS
Restricted areas denote the existence of unusual, often invisible hazards to aircraft such as artillery firing, aerial gunnery, or guided missiles. An aircraft may not enter a restricted area unless permission has been obtained from the controlling agency. Restricted areas are depicted on aeronautical charts and are published in the Federal Register.

WARNING AREAS
Warning areas consist of airspace, which may contain hazards to nonparticipating aircraft in international airspace. The activities may be much the same as those for a restricted area. Warning areas are established beyond the 3-mile limit. Warning areas are depicted on aeronautical charts.

MILITARY OPERATION AREAS
Military operation areas (MOA) consist of airspace of defined vertical and lateral limits established for the purpose of separating certain military training activity from IFR traffic. There is no restriction against a pilot operating VFR in these areas; however, a pilot should be alert since training activities may include acrobatic and abrupt maneuvers. MOAs are depicted on aeronautical charts.

ALERT AREAS
Alert areas are depicted on aeronautical charts and are to advise pilots that a high volume of pilot training or unusual aerial activity is taking place.

CONTROLLED FIRING AREAS
Controlled firing areas contain activities, which, if not conducted in a controlled environment, could be hazardous to nonparticipating aircraft. The difference between controlled firing areas and other special use airspace is that activities must be suspended when a spotter aircraft, radar, or ground lookout position indicates an aircraft might be approaching the area.

CONTROLLED AIRSPACE

Controlled airspace is a generic term that covers the different classifications of airspace and defined dimensions within which air traffic control service is provided in accordance with the airspace classification.

Controlled airspace consists of:

• Class A
• Class B
• Class C
• Class D
• Class E

CLASS A AIRSPACE
Class A airspace is generally the airspace from 18,000 feet mean sea level (MSL) up to and including FL600, including the airspace overlying the waters within 12 nautical miles (NM) of the coast of the 48 contiguous states and Alaska. Unless otherwise authorized, all operation in Class A airspace will be conducted under instrument flight rules (IFR).

CLASS B AIRSPACE
Class B airspace is generally the airspace from the surface to 10,000 feet MSL surrounding the nation's busiest airports. The configuration of Class B airspace is individually tailored to the needs of a particular area and consists of a surface area and two or more layers. Some Class B airspace resembles an upside-down wedding cake. At least a private pilot certificate is required to operate in Class B airspace; however, there is an exception to this requirement. Student pilots or recreational pilots seeking private pilot certification may operate in the airspace and land at other than specified primary airports within the airspace if they have received training and had their logbook endorsed by a certified flight instructor.

CLASS C AIRSPACE
Class C airspace generally extends from the surface to 4,000 feet above the airport elevation surrounding those airports having an operational control tower, that are serviced by a radar approach control, and with a certain number of IFR operations or passenger enplanements. This airspace is charted in feet MSL, and is generally of a 5 NM radius surface area that extends from the surface to 4,000 feet above the airport elevation, and a 10 NM radius area that extends from 1,200 feet to 4,000 feet above the airport elevation. There is also an outer area with a 20 NM radius, which extends from the surface to 4,000 feet above the primary airport, and this area may include one or more satellite airports.

CLASS D AIRSPACE
Class D airspace generally extends from the surface to 2,500 feet above the airport elevation surrounding those airports that have an operational control tower. The configuration of Class D airspace will be tailored to meet the operational needs of the area.

CLASS E AIRSPACE
Class E airspace is generally controlled airspace that is not designated A, B, C, or D. Except for 18,000 feet MSL, Class E airspace has no defined vertical limit, but rather it extends upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace.

COLLISION AVOIDANCE

The pilot can contribute to collision avoidance by being alert and scanning for other aircraft. This is particularly important in the vicinity of an airport. Effective scanning is accomplished with a series of short, regularly spaced eye movements that bring successive areas of the sky into the central visual field.

Each movement should not exceed 10°, and each should be observed for at least 1 second to enable detection. Although back and forth eye movements seem preferred by most pilots, each pilot should develop a scanning pattern that is most comfortable and then adhere to it to assure optimum scanning. Even if entitled to the right-of-way, a pilot should give way if it is felt another aircraft is too close.

CLEARING PROCEDURES
The following procedures and considerations should assist a pilot in collision avoidance under various situations.

• Before Takeoff—Prior to taxiing onto a runway or landing area in preparation for takeoff, pilots should scan the approach area for possible landing traffic, executing appropriate maneuvers to provide a clear view of the approach areas.
• Climbs and Descents—During climbs and descents in flight conditions which permit visual detection of other traffic, pilots should execute gentle banks left and right at a frequency which permits continuous visual scanning of the airspace.
• Straight and Level—During sustained periods of straight-and-level flight, a pilot should execute appropriate clearing procedures at periodic intervals.
• Traffic Patterns—Entries into traffic patterns while descending should be avoided.
• Traffic at VOR Sites—Due to converging traffic, sustained vigilance should be maintained in the vicinity of VORs and intersections.
• Training Operations—Vigilance should be maintained and clearing turns should be made prior to a practice maneuver. During instruction, the pilot should be asked to verbalize the clearing procedures (call out "clear left, right, above, and below").

High-wing and low-wing aircraft have their respective blind spots. High-wing aircraft should momentarily raise their wing in the direction of the intended turn and look for traffic prior to commencing the turn. Lowwing aircraft should momentarily lower the wing.

RUNWAY INCURSION AVOIDANCE
It is important to give the same attention to operating on the surface as in other phases of flights. Proper planning can prevent runway incursions and the possibility of a ground collision. A pilot should be aware of the airplane's position on the surface at all times and be aware of other aircraft and vehicle operations on the airport. At times controlled airports can be busy and taxi instructions complex. In this situation it may be advisable to write down taxi instructions. The following are some practices to help prevent a runway incursion.

• Read back all runway crossing and/or hold instructions.
• Review airport layouts as part of preflight planning and before descending to land, and while taxiing as needed.
• Know airport signage.
• Review Notices to Airmen (NOTAM) for information on runway/taxiway closures and construction areas.
• Request progressive taxi instructions from ATC when unsure of the taxi route.
• Check for traffic before crossing any Runway Hold Line and before entering a taxiway.
• Turn on aircraft lights and the rotating beacon or strobe lights while taxing.
• When landing, clear the active runway as soon as possible, then wait for taxi instructions before further movement.
• Study and use proper phraseology in order to understand and respond to ground control instructions.
• Write down complex taxi instructions at unfamiliar airports.

WAKE TURBULENCE

All aircraft generate a wake while in flight. A pair of counter-rotating vortices trailing from the wingtips causes this disturbance. The vortices from larger aircraft pose problems to encountering aircraft. The wake of these aircraft can impose rolling moments exceeding the roll-control authority of the encountering aircraft. Also, the turbulence generated within the vortices can damage aircraft components and equipment if encountered at close range. For this reason, a pilot must envision the location of the vortex wake and adjust the flightpath accordingly.

During ground operations and during takeoff, jet-engine blast (thrust stream turbulence) can cause damage and upsets at close range. For this reason, pilots of small aircraft should consider the effects of jet-engine blast and maintain adequate separation. Also, pilots of larger aircraft should consider the effects of their aircraft's jet-engine blast on other aircraft and equipment on the ground.

VORTEX GENERATION
Lift is generated by the creation of a pressure differential over the wing surface. The lowest pressure occurs over the upper wing surface, and the highest pressure under the wing. This pressure differential triggers the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips. After the rollup is completed, the wake consists of two counter-rotating cylindrical vortices. Most of the energy is within a few feet of the center of each vortex, but pilots should avoid a region within about 100 feet of the vortex core.

VORTEX STRENGTH
The weight, speed, and shape of the wing of the generating aircraft govern the strength of the vortex. The vortex characteristics of any given aircraft can also be changed by the extension of flaps or other wing configuration devices as well as by a change in speed. The greatest vortex strength occurs when the generating aircraft is heavy, clean, and slow.

VORTEX BEHAVIOR
Trailing vortices have certain behavioral characteristics that can help a pilot visualize the wake location and take avoidance precautions. Vortices are generated from the moment an aircraft leaves the ground, since trailing vortices are the byproduct of wing lift. The vortex circulation is outward, upward, and around the wingtips when viewed from either ahead or behind the aircraft. Tests have shown that vortices remain spaced a bit less than a wingspan apart, drifting with the wind, at altitudes greater than a wingspan from the ground. Tests have also shown that the vortices sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft.

When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move laterally over the ground at a speed of 2 or 3 knots. A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. A tailwind condition can move the vortices of the preceding aircraft forward into the touchdown zone.

VORTEX AVOIDANCE PROCEDURES

• Landing behind a larger aircraft on the same runway—stay at or above the larger aircraft's approach flight-path and land beyond its touchdown point.
• Landing behind a larger aircraft on a parallel runway closer than 2,500 feet—consider the possibility of drift and stay at or above the larger aircraft's final approach flight-path and note its touchdown point.
• Landing behind a larger aircraft on crossing runway—cross above the larger aircraft's flight-path.
• Landing behind a departing aircraft on the same runway—land prior to the departing aircraft's rotating point.
• Landing behind a larger aircraft on a crossing runway—note the aircraft's rotation point and if past the intersection, continue and land prior to the intersection. If the larger aircraft rotates prior to the intersection, avoid flight below its flight-path. Abandon the approach unless a landing is ensured well before reaching the intersection.
• Departing behind a large aircraft, rotate prior to the large aircraft's rotation point and climb above its climb path until turning clear of the wake.
• For intersection takeoffs on the same runway, be alert to adjacent larger aircraft operations, particularly upwind of the runway of intended use. If an intersection takeoff clearance is received, avoid headings that will cross below the larger aircraft's path.
• If departing or landing after a large aircraft executing a low approach, missed approach, or touch and go landing (since vortices settle and move laterally near the ground, the vortex hazard may exist along the runway and in the flight-path, particularly in a quartering tailwind). It is prudent to wait 2 minutes prior to a takeoff or landing.
• En route it is advisable to avoid a path below and behind a large aircraft, and if a large aircraft is observed above on the same track, change the aircraft position laterally and preferably upwind.

AIR TRAFFIC CONTROL SERVICES

Besides the services provided by FSS, there are numerous other services provided by ATC. In many instances a pilot is required to have contact with air traffic control, but even when not required, a pilot will find it helpful to request their services.

PRIMARY RADAR
Radar is a method whereby radio waves are transmitted into the air and are then received when they have been reflected by an object in the path of the beam. Range is determined by measuring the time it takes (at the speed of light) for the radio wave to go out to the object and then return to the receiving antenna. The direction of a detected object from a radar site is determined by the position of the rotating antenna when the reflected portion of the radio wave is received.

Modern radar is very reliable and there are seldom outages. This is due to reliable maintenance and improved equipment. There are, however, some limitations which may affect air traffic control services and prevent a controller from issuing advisories concerning aircraft which are not under their control and cannot be seen on radar.

The characteristics of radio waves are such that they normally travel in a continuous straight line unless they are "bent" by atmospheric phenomena such as temperature inversions, reflected or attenuated by dense objects such as heavy clouds and precipitation, or screened by high terrain features.

AIR TRAFFIC CONTROL RADAR BEACON SYSTEM
The air traffic control radar beacon system (ATCRBS) is often referred to as "secondary surveillance radar." This system consists of three components and helps in alleviating some of the limitations associated with primary radar. The three components are an interrogator, transponder, and radarscope. The advantages of ATCRBS are the reinforcement of radar targets, rapid target identification, and a unique display of selected codes.

TRANSPONDER
The transponder is the airborne portion of the secondary surveillance radar system and a system with which a pilot should be familiar. The ATCRBS cannot display the secondary information unless an aircraft is equipped with a transponder. A transponder is also required to operate in certain controlled airspace.

A transponder code consists of four numbers from zero to seven (4,096 possible codes). There are some standard codes, or ATC may issue a four-digit code to an aircraft. When a controller requests a code or function on the transponder, the word "squawk" may be used.

RADAR TRAFFIC INFORMATION SERVICE
Radar equipped air traffic control facilities provide radar assistance to VFR aircraft provided the aircraft can communicate with the facility and are within radar coverage. This basic service includes safety alerts, traffic advisories, limited vectoring when requested and sequencing at locations where this procedure has been established. In addition to basic radar service, terminal radar service area (TRSA) has been implemented at certain terminal locations. The purpose of this service is to provide separation between all participating VFR aircraft and all IFR aircraft operating within the TRSA.

Class C service provides approved separation between IFR and VFR aircraft, and sequencing of VFR aircraft to the primary airport. Class B service provides approved separation of aircraft based on IFR, VFR, and/or weight, and sequencing of VFR arrivals to the primary airport(s).

ATC issues traffic information based on observed radar targets. The traffic is referenced by azimuth from the aircraft in terms of the 12-hour clock. Also the distance in nautical miles, direction in which the target is moving, and the type and altitude of the aircraft, if known, are given. An example would be: "Traffic 10 o'clock 5 miles east bound, Cessna 152, 3,000 feet." The pilot should note that traffic position is based on the aircraft track, and that wind correction can affect the clock position at which a pilot locates traffic.

RADIO COMMUNICATIONS

Operating in and out of a controlled airport, as well as in a good portion of the airspace system, requires that an aircraft have two-way radio communication capability. For this reason, a pilot should be knowledgeable of radio station license requirements and radio communications equipment and procedures.

RADIO LICENSE
There is no license requirement for a pilot operating in the United States; however, a pilot who operates internationally is required to hold a restricted radiotelephone permit issued by the Federal Communications Commission (FCC). There is also no station license requirement for most general aviation aircraft operating in the United States. A station license is required however for an aircraft which is operating internationally, which uses other than a very high frequency (VHF) radio, and which meets other criteria.

RADIO EQUIPMENT
In general aviation, the most common types of radios are VHF. A VHF radio operates on frequencies between 118.0 and 136.975 and is classified as 720 or 760 depending on the number of channels it can accommodate. The 720 and 760 uses .025 spacing (118.025, 118.050) with the 720 having a frequency range up to 135.975 and the 760 going up to 136.975.

VHF radios are limited to line of sight transmissions; therefore, aircraft at higher altitudes are able to transmit and receive at greater distances. Using proper radio phraseology and procedures will contribute to a pilot's ability to operate safely and efficiently in the airspace system. A review of the Pilot/Controller Glossary contained in the Aeronautical Information Manual (AIM) will assist a pilot in the use and understanding of standard terminology.

The AIM also contains many examples of radio communications, which should be helpful. The International Civil Aviation Organization (ICAO) has adopted a phonetic alphabet, which should be used in radio communications. When communicating with ATC, pilots should use this alphabet to identify their aircraft.

LOST COMMUNICATION PROCEDURES
It is possible that a pilot might experience a malfunction of the radio. This might cause the transmitter, receiver, or both to become inoperative. If a receiver becomes inoperative and a pilot needs to land at a controlled airport, it is advisable to remain outside or above Class D airspace until the direction and flow of traffic is determined. A pilot should then advise the tower of the aircraft type, position, altitude, and intention to land. The pilot should continue, enter the pattern, report a position as appropriate, and watch for light signals from the tower. Light signal colors and their meanings are contained in figure 12-14.

If the transmitter becomes inoperative, a pilot should follow the previously stated procedures and also monitor the appropriate air traffic control frequency. During daylight hours air traffic control transmissions may be acknowledged by rocking the wings, and at night by blinking the landing light. When both receiver and transmitter are inoperative, the pilot should remain outside of Class D airspace until the flow of traffic has been determined and then enter the pattern and watch for light signals. If a radio malfunctions prior to departure, it is advisable to have it repaired, if possible. If this is not possible, a call should be made to air traffic control and the pilot should request authorization to depart without two-way radio communications. If authorization is given to depart, the pilot will be advised to monitor the appropriate frequency and/or watch for light signals as appropriate.

WIND DIRECTION INDICATORS

It is important for a pilot to know the direction of the wind. At facilities with an operating control tower, this information is provided by ATC. Information may also be provided by FSS personnel located at a particular airport or by requesting information on a common traffic advisory frequency (CTAF) at airports that have the capacity to receive and broadcast on this frequency.

When none of these services is available, it is possible to determine wind direction and runway in use by visual wind indicators. A pilot should check these wind indicators even when information is provided on the CTAF at a given airport because there is no assurance that the information provided is accurate. Wind direction indicators include a wind sock, wind tee, or tetrahedron. These are usually located in a central location near the runway and may be placed in the center of a segmented circle, which will identify the traffic pattern direction, if it is other than the standard left-hand pattern.

The windsock is a good source of information since it not only indicates wind direction, but also allows the pilot to estimate the wind velocity and gusts or factor. The windsock extends out straighter in strong winds and will tend to move back and forth when the wind is gusty. Wind tees and tetrahedrons can swing freely, and will align themselves with the wind direction. The wind tee and tetrahedron can also be manually set to align with the runway in use; therefore, a pilot should also look at the windsock, if available.

AIRPORT LIGHTING

The majority of airports have some type of lighting for night operations. The variety and type of lighting systems depends on the volume and complexity of operations at a given airport. Airport lighting is standardized so that airports use the same light colors for runways and taxiways.

AIRPORT BEACON
Airport beacons help a pilot identify an airport at night. The beacons are operated from dusk till dawn and sometimes they are turned on if the ceiling is less than 1,000 feet and/or the ground visibility is less than 3 statute miles (visual flight rules minimums). However, there is no requirement for this, so a pilot has the responsibility of determining if the weather is VFR.

The beacon has a vertical light distribution to make it most effective from 1-10° above the horizon, although it can be seen well above or below this spread. The beacon may be an omnidirectional capacitor-discharge device, or it may rotate at a constant speed, which produces the visual effect of flashes at regular intervals.
The combination of light colors from an airport beacon indicates the type of airport.

Some of the most common beacons are:

• Flashing white and green for civilian land airports.
• Flashing white and yellow for a water airport.
• Flashing white, yellow, and green for a heliport.
• Two quick white flashes followed by a green flash identifies a military airport.

APPROACH LIGHT SYSTEMS
Approach light systems are primarily intended to provide a means to transition from instrument flight to visual flight for landing. The system configuration depends on whether the runway is a precision or nonprecision instrument runway. Some systems include sequenced flashing lights, which appear to the pilot as a ball of light traveling toward the runway at high speed. Approach lights can also aid pilots operating under VFR at night.

VISUAL GLIDESLOPE INDICATORS
Visual glideslope indicators provide the pilot with glidepath information that can be used for day or night approaches. By maintaining the proper glidepath as provided by the system, a pilot should have adequate obstacle clearance and should touch down within a specified portion of the runway.

VISUAL APPROACH SLOPE INDICATOR
Visual approach slope indicator (VASI) installations are the most common visual glidepath systems in use. The VASI provides obstruction clearance within 10° of the runway extended runway centerline, and to 4 nautical miles (NM) from the runway threshold. AVASI consists of light units arranged in bars. There are 2-bar and 3-bar VASIs. The 2-bar VASI has near and far light bars and the 3-bar VASI has near, middle, and far light bars. Two-bar VASI installations provide one visual glidepath which is normally set at 3°. The 3-bar system provides two glidepaths with the lower glidepath normally set at 3° and the upper glidepath one-fourth degree above the lower glidepath.

The basic principle of the VASI is that of color differentiation between red and white. Each light unit projects a beam of light having a white segment in the upper part of the beam and a red segment in the lower part of the beam.

OTHER GLIDEPATH SYSTEMS
A precision approach path indicator (PAPI) uses lights similar to the VASI system except they are installed in a single row, normally on the left side of the runway. A tri-color system consists of a single light unit projecting a three-color visual approach path. A below the glidepath indication is red, on the glidepath color is green, and above the glidepath is indicated by amber.

When descending below the glidepath, there is a small area of dark amber. Pilots should not mistake this area for an "above the glidepath" indication.

There are also pulsating systems, which consist of a single light unit projecting a two-color visual approach path. A below the glidepath indication is shown by a steady red light, slightly below is indicated by pulsating red, on the glidepath is indicated by a steady white light, and a pulsating white light indicates above the glidepath.

RUNWAY LIGHTING
There are various lights that identify parts of the runway complex. These assist a pilot in safely making a takeoff or landing during night operations.

RUNWAY END IDENTIFIER LIGHTS
Runway end identifier lights (REIL) are installed at many airfields to provide rapid and positive identification of the approach end of a particular runway. The system consists of a pair of synchronized flashing lights located laterally on each side of the runway threshold. REILs may be either omnidirectional or unidirectional facing the approach area.

RUNWAY EDGE LIGHTS
Runway edge lights are used to outline the edges of runways at night or during low visibility conditions. These lights are classified according to the intensity they are capable of producing. They are classified as high intensity runway lights (HIRL), medium intensity runway lights (MIRL), or low intensity runway lights (LIRL). The HIRL and MIRL have variable intensity settings. These lights are white, except on instrument runways, where amber lights are used on the last 2,000 feet or half the length of the runway, whichever is less. The lights marking the end of the runway are red.

IN-RUNWAY LIGHTING
Touchdown zone lights (TDZL), runway centerline lights (RCLS), and taxiway turnoff lights are installed on some precision runways to facilitate landing under adverse visibility conditions. TDZLs are two rows of transverse light bars disposed symmetrically about the runway centerline in the runway touchdown zone. RCLS consists of flush centerline lights spaced at 50-foot intervals beginning 75 feet from the landing threshold. Taxiway turnoff lights are flush lights, which emit a steady green color.

CONTROL OF AIRPORT LIGHTING
Airport lighting is controlled by air traffic controllers at controlled airports. At uncontrolled airports, the lights may be on a timer, or where an FSS is located at an airport, the FSS personnel may control the lighting. A pilot may request various light systems be turned on or off and also request a specified intensity, if available, from ATC or FSS personnel. At selected uncontrolled airports, the pilot may control the lighting by using the radio. This is done by selecting a specified frequency and clicking the radio microphone.

For information on pilot controlled lighting at various airports, refer to the Airport/Facility Directory.

TAXIWAY LIGHTS
Omnidirectional taxiway lights outline the edges of the taxiway and are blue in color. At many airports, these edge lights may have variable intensity settings that may be adjusted by an air traffic controller when deemed necessary or when requested by the pilot. Some airports also have taxiway centerline lights that are green in color.

OBSTRUCTION LIGHTS
Obstructions are marked or lighted to warn pilots of their presence during daytime and nighttime conditions.

Obstruction lighting can be found both on and off an airport to identify obstructions. They may be marked or lighted in any of the following conditions.

• Red Obstruction Lights—either flash or emit a steady red color during nighttime operations, and the obstructions are painted orange and white for daytime operations.
• High Intensity White Obstruction Light— flashes high intensity white lights during the daytime with the intensity reduced for nighttime.
• Dual Lighting—is a combination of flashing red beacons and steady red lights for nighttime operation, and high intensity white lights for daytime operations.

AIRPORT MARKINGS AND SIGNS

There are markings and signs used at airports, which provide directions and assist pilots in airport operations.

Some of the most common markings and signs will be discussed. Additional information may be found in the Aeronautical Information Manual (AIM).

RUNWAY MARKINGS
Runway markings vary depending on the type of operations conducted at the airport. A basic VFR runway may only have centerline markings and runway numbers.

Since aircraft are affected by the wind during takeoffs and landings, runways are laid out according to the local prevailing winds. Runway numbers are in reference to magnetic north. Certain airports have two or even three runways laid out in the same direction.

These are referred to as parallel runways and are distinguished by a letter being added to the runway number.

Examples are runway 36L (left), 36C (center), and 36R (right).

Another feature of some runways is a displaced threshold. A threshold may be displaced because of an obstruction near the end of the runway. Although this portion of the runway is not to be used for landing, it may be available for taxiing, takeoff, or landing rollout.

Some airports may have a blast pad/stopway area. The blast pad is an area where a propeller or jet blast can dissipate without creating a hazard. The stopway area is paved in order to provide space for an airplane to decelerate and stop in the event of an aborted takeoff. These areas cannot be used for takeoff or landing.

TAXIWAY MARKINGS
Airplanes use taxiways to transition from parking areas to the runway. Taxiways are identified by a continuous yellow centerline stripe. A taxiway may include edge markings to define the edge of the taxiway. This is usually done when the taxiway edge does not correspond with the edge of the pavement. If an edge marking is a continuous line, the paved shoulder is not intended to be used by an airplane. If it is a dashed marking, an airplane may use that portion of the pavement. Where a taxiway approaches a runway, there may be a holding position marker. These consist of four yellow lines (two solid and two dashed). The solid lines are where the airplane is to hold. At some controlled airports, holding position markings may be found on a runway. They are used when there are intersecting runways, and air traffic control issues instructions such as "cleared to land—hold short of runway 30."

OTHER MARKINGS
Some of the other markings found on the airport include vehicle roadway markings, VOR receiver checkpoint markings, and non-movement area boundary markings. Vehicle roadway markings are used when necessary to define a pathway for vehicle crossing areas that are also intended for aircraft. These markings usually consist of a solid white line to delineate each edge of the roadway and a dashed line to separate lanes within the edges of the roadway.

A VOR receiver checkpoint marking consists of a painted circle with an arrow in the middle. The arrow is aligned in the direction of the checkpoint azimuth. This allows pilots to check aircraft instruments with navigational aid signals.

A non-movement area boundary marking delineates a movement area under air traffic control. These markings are yellow and located on the boundary between the movement and non-movement area. They normally consist of two yellow lines (one solid and one dashed).

AIRPORT SIGNS
There are six types of signs that may be found at airports. The more complex the layout of an airport, the more important the signs become to pilots.

The six types of signs are:

• Mandatory Instruction Signs—have a red background with a white inscription. These signs denote an entrance to a runway, a critical area, or a prohibited area.
• Location Signs—are black with yellow inscription and a yellow border and do not have arrows. They are used to identify a taxiway or runway location, to identify the boundary of the runway, or identify an instrument landing system (ILS) critical area.
• Direction Signs—have a yellow background with black inscription. The inscription identifies the designation of the intersecting taxiway(s) leading out of an intersection.
• Destination Signs—have a yellow background with black inscription and also contain arrows. These signs provide information on locating things, such as runways, terminals, cargo areas, and civil aviation areas.
• Information Signs—have a yellow background with black inscription. These signs are used to provide the pilot with information on such things as areas that cannot be seen from the control tower, applicable radio frequencies, and noise abatement procedures. The airport operator determines the need, size, and location of these signs.
• Runway Distance Remaining Signs—have a black background with white numbers. The numbers indicate the distance of the remaining runway in thousands of feet.

SOURCES FOR AIRPORT DATA

When a pilot flies into a different airport, it is important to review the current data for that airport. This data can provide the pilot with information, such as communication frequencies, services available, closed runways, or airport construction. Three common sources of information are:

• Aeronautical Charts
• Airport/Facility Directory (A/FD)
• Notices to Airmen (NOTAMs)

AIRPORT/FACILITY DIRECTORY
The Airport/Facility Directory (A/FD) provides the most comprehensive information on a given airport. It contains information on airports, heliports, and seaplane bases that are open to the public. The A/FDs are contained in seven books, which are organized by regions. These A/FDs are revised every 8 weeks.

NOTICES TO AIRMEN
Notices to Airmen (NOTAMs) provide the most current information available. They provide time-critical information on airports and changes that affect the national airspace system and are of concern to instrument flight rule (IFR) operations. NOTAM information is classified into three categories. These are NOTAM-D or distant, NOTAM-L or local, and flight data center (FDC) NOTAMs. NOTAM-Ds are attached to hourly weather reports and are available at flight service stations (AFSS/FSS). NOTAM-Ls include items of a local nature, such as taxiway closures or construction near a runway.

These NOTAMs are maintained at the FSS nearest the airport affected. NOTAM-Ls must be requested from an FSS other than the one nearest the local airport for which the NOTAM was issued. FDC NOTAMs are issued by the National Flight Data Center and contain regulatory information, such as temporary flight restrictions or an amendment to instrument approach procedures. The NOTAM-Ds and FDC NOTAMs are contained in the Notices to Airmen publication, which is issued every 28 days. Prior to any flight, pilots should check for any NOTAMs that could affect their intended flight.

TYPES OF AIRPORTS

There are two types of airports:

• • Controlled Airport
• • Uncontrolled Airport

CONTROLLED AIRPORT
A controlled airport has an operating control tower. Air traffic control (ATC) is responsible for providing for the safe, orderly, and expeditious flow of air traffic at airports where the type of operations and/or volume of traffic requires such a service. Pilots operating from a controlled airport are required to maintain two-way radio communication with air traffic controllers, and to acknowledge and comply with their instructions.

Pilots must advise ATC if they cannot comply with the instructions issued and request amended instructions. A pilot may deviate from an air traffic instruction in an emergency, but must advise ATC of the deviation as soon as possible.

UNCONTROLLED AIRPORT
An uncontrolled airport does not have an operating control tower. Two-way radio communications are not required, although it is a good operating practice for pilots to transmit their intentions on the specified frequency for the benefit of other traffic in the area.

WEATHER CHARTS

Weather charts are graphic charts that depict current or forecast weather. They provide an overall picture of the United States and should be used in the beginning stages of flight planning. Typically, weather charts show the movement of major weather systems and fronts. Surface analysis, weather depiction, and radar summary charts are sources of current weather information. Significant weather prognostic charts provide an overall forecast weather picture.

SURFACE ANALYSIS CHART
The surface analysis chart, depicts an analysis of the current surface weather. This chart is a computer prepared report that is transmitted every 3 hours and covers the contiguous 48 states and adjacent areas. A surface analysis chart shows the areas of high and low pressure fronts, temperatures, dewpoints, wind directions and speeds, local weather, and visual obstructions.

Surface weather observations for reporting points across the United States are also depicted on this chart. A station model illustrates each of these reporting points. A station model will include:

• Type of Observation—A round model indicates an official weather observer made the observation. A square model indicates the observation is from an automated station. Stations located offshore give data from ships, buoys, or offshore platforms.
• Sky Cover—The station model depicts total sky cover and will be shown as clear, scattered, broken, overcast, or obscured/partially obscured.
• Clouds—Cloud types are represented by specific symbols. Low cloud symbols are placed beneath the station model, while middle and high cloud symbols are placed directly above the station model. Typically, only one type of cloud will be depicted with the station model.
• Sea Level Pressure—Sea level pressure given in three digits to the nearest tenth of a millibar. For 1000 mbs or greater, prefix a 10 to the three digits. For less than 1000 mbs, prefix a 9 to the three digits.
• Pressure Change/Tendency—Pressure change in tenths of millibars over the past 3 hours. This is depicted directly below the sea level pressure.
• Precipitation—A record of the precipitation that has fallen over the last 6 hours to the nearest hundredth of an inch.
• Dewpoint—Dewpoint is given in degrees Fahrenheit.
• Present Weather—Over 100 different weather symbols are used to describe the current weather.
• Temperature—Temperature is given in degrees Fahrenheit.
• Wind—True direction of wind is given by the wind pointer line, indicating the direction from which the wind is coming. A short barb is equal to 5 knots of wind, a long barb is equal to 10 knots of wind, and a pennant is equal to 50 knots.

WEATHER DEPICTION CHART
A weather depiction chart details surface conditions as derived from METAR and other surface observations.

The weather depiction chart is prepared and transmitted by computer every 3 hours beginning at 0100 Zulu time, and is valid at the time of the plotted data. It is designed to be used for flight planning by giving an overall picture of the weather across the United States.

This type of chart typically displays major fronts or areas of high and low pressure. The weather depiction chart also provides a graphic display of IFR, VFR, and MVFR (marginal VFR) weather. Areas of IFR conditions (ceilings less than 1,000 feet and visibility less than 3 miles) are shown by a hatched area outlined by a smooth line. MVFR regions (ceilings 1,000 to 3,000 feet, visibility 3 to 5 miles) are shown by a non-hatched area outlined by a smooth line. Areas of VFR (no ceiling or ceiling greater than 3,000 feet and visibility greater than 5 miles) are not outlined.

Weather depiction charts show a modified station model that provides sky conditions in the form of total sky cover, cloud height or ceiling, weather, and obstructions to visibility, but does not include winds or pressure readings like the surface analysis chart. A bracket ( ] ) symbol to the right of the station indicates the observation was made by an automated station. A detailed explanation of a station model is depicted in the previous discussion of surface analysis charts.

RADAR SUMMARY CHART
A radar summary chart is a graphically depicted collection of radar weather reports (SDs). The chart is published hourly at 35 minutes past the hour. It displays areas of precipitation as well as information regarding the characteristics of the precipitation. A radar summary chart includes:

• No information—If information is not reported, the chart will say "NA." If no echoes are detected, the chart will say "NE."
• Precipitation intensity contours—Intensity can be described as one of six levels and is shown on the chart by three contour intervals.
• Height of tops—The heights of the echo tops are given in hundreds of feet MSL.
• Movement of cells—Individual cell movement is indicated by an arrow pointing in the direction of movement. The speed of movement in knots is the number at the top of the arrow head. "LM" indicates little movement.
• Type of precipitation—The type of precipitation is marked on the chart using specific symbols. These symbols are not the same as used on the METAR charts.
• Echo configuration—Echoes are shown as being areas, cells, or lines.
• Weather watches—Severe weather watch areas for tornadoes and severe thunderstorms are depicted by boxes outlined with heavy dashed lines. The radar summary chart is a valuable tool for preflight planning. It does, however, contain several limitations for the usage of the chart. This chart depicts only areas of precipitation. It will not show areas of clouds and fog with no appreciable precipitation, or the height of the tops and bases of the clouds. Radar summary charts are a depiction of current precipitation and should be used in conjunction with current METAR and weather forecasts.

SIGNIFICANT WEATHER PROGNOSTIC CHARTS
Significant Weather Prognostic Charts are available for low-level significant weather from the surface to FL240 (24,000 feet), also referred to as the 400 millibar level, and high-level significant weather from FL250 to FL600 (25,000 to 60,000 feet). The primary concern of this discussion is the low-level significant weather prognostic chart.

The low-level chart comes in two forms: the 12- and 24-hour forecast chart, and the 36 and 48 surface only forecast chart. The first chart is a four-panel chart that includes 12- and 24-hour forecasts for significant weather and surface weather. Charts are issued four times a day at 0000Z, 0600Z, 1200Z, and 1800Z. The valid time for the chart is printed on the lower left-hand corner of each panel.

The upper two panels show forecast significant weather, which may include nonconvective turbulence, freezing levels, and IFR or MVFR weather. Areas of moderate or greater turbulence are enclosed in dashed lines. Numbers within these areas give the height of the turbulence in hundreds of feet MSL. Figures below the line show the anticipated base, while figures above the line show the top of the zone of turbulence. Also shown on this panel are areas of VFR, IFR, and MVFR. IFR areas are enclosed by solid lines, MVFR areas are enclosed by scalloped lines, and the remaining, unenclosed area is designated VFR. Zigzag lines and the letters "SFC" indicate freezing levels in that area are at the surface. Freezing level height contours for the highest freezing level are drawn at 4,000-foot intervals with dashed lines.

The lower two panels show the forecast surface weather and depicts the forecast locations and characteristics of pressure systems, fronts, and precipitation. Standard symbols are used to show fronts and pressure centers. Direction of movement of the pressure center is depicted by an arrow. The speed, in knots, is shown next to the arrow. In addition, areas of forecast precipitation and thunderstorms are outlined.

Areas of precipitation that are shaded indicate at least one-half of the area is being affected by the precipitation.

Unique symbols indicate the type of precipitation and the manner in which it occurs.

Prognostic charts are an excellent source of information for preflight planning; however, this chart should be viewed in light of current conditions and specific local area forecasts.

The 36- and 48-hour significant weather prognostic chart is an extension of the 12- and 24-hour forecast. It provides information regarding only surface weather forecasts and includes a discussion of the forecast. This chart is issued only two times a day. It typically contains forecast positions and characteristics of pressure patterns, fronts, and precipitation.

AVIATION FORECASTS

Observed weather condition reports are often used in the creation of forecasts for the same area. A variety of different forecast products are produced and designed to be used in the preflight planning stage. The printed forecasts that pilots need to be familiar with are the terminal aerodrome forecast (TAF), aviation area forecast (FA), in-flight weather advisories (SIGMET, AIRMET), and the winds and temperatures aloft forecast (FD).

TERMINAL AERODROME FORECASTS (TAF)
A terminal aerodrome forecast is a report established for the 5 statute mile radius around an airport. TAF reports are usually given for larger airports. Each TAF is valid for a 24-hour time period, and is updated four times a day at 0000Z, 0600Z, 1200Z, and 1800Z. The TAF utilizes the same descriptors and abbreviations as used in the METAR report.

The terminal forecast includes the following information in sequential order:

1. Type of Report—A TAF can be either a routine forecast (TAF) or an amended forecast (TAF AMD).
2. ICAO Station Identifier—The station identifier is the same as that used in a METAR.
3. Date and Time of Origin—Time and date of TAF origination is given in the six-number code with the first two being the date, the last four being the time. Time is always given in UTC as denoted by the Z following the number group.
4. Valid Period Date and Time—The valid forecast time period is given by a six-digit number group. The first two numbers indicate the date, followed by the two-digit beginning time for the valid period, and the last two digits are the ending time.
5. Forecast Wind—The wind direction and speed forecast are given in a five-digit number group. The first three indicate the direction of the wind in reference to true north. The last two digits state the windspeed in knots as denoted by the letters "KT." Like the METAR, winds greater than 99 knots are given in three digits.
6. Forecast Visibility—The forecast visibility is given in statute miles and may be in whole numbers or fractions. If the forecast is greater than 6 miles, it will be coded as "P6SM."
7. Forecast Significant Weather—Weather phenomenon is coded in the TAF reports in the same format as the METAR. If no significant weather is expected during the forecast time period, the denotation "NSW" will be included in the "becoming" or "temporary" weather groups.
8. Forecast Sky Condition—Forecast sky conditions are given in the same manner as the METAR. Only cumulonimbus (CB) clouds are forecast in this portion of the TAF report as opposed to CBs and towering cumulus in the METAR.
9. Forecast Change Group—For any significant weather change forecast to occur during the TAF time period, the expected conditions and time period are included in thisgroup. This information may be shown as From (FM), Becoming (BECMG), and Temporary (TEMPO). "From" is used when a rapid and significant change, usually within an hour, is expected. "Becoming" is used when a gradual change in the weather is expected over a period of no more than 2 hours. "Temporary" is used for temporary fluctuations of weather, expected to last for less than an hour.
10. Probability Forecast—The probability forecast is given percentage that describes the probability of thunderstorms and precipitation occurring in the coming hours. This forecast is not used for the first 6 hours of the 24-hour forecast.

Example:
TAF
KPIR 111130Z 111212 15012KT P6SM BKN090
TEMPO 1214 5SM BR
FM1500 16015G25KT P6SM SCT040 BKN250
FM0000 14012KT P6SM BKN080 OVC150 PROB40
0004 3SM TSRA BKN030CB
FM0400 1408KT P6SM SCT040 OVC080 TEMPO
0408 3SM TSRA OVC030CB
BECMG 0810 32007KT=

Explanation:
Routine TAF for Pierre, South Dakota...on the 11th day of the month, at 1130Z...valid for 24 hours from 1200Z on the 11th to 1200Z on the 12th ...wind from 150° at 12 knots...visibility greater than 6 statute miles...broken clouds at 9,000 feet...temporarily, between 1200Z and 1400Z, visibility 5 statute miles in mist...from 1500Z winds from 160° at 15 knots, gusting to 25 knots visibility greater than 6 statute miles...clouds scattered at 4,000 feet and broken at 25,000 feet...from 0000Z wind from 140° at 12 knots...visibility greater than 6 statute miles...clouds broken at 8,000 feet, overcast at 15,000 feet...between 0000Z and 0400Z, there is 40 percent probability of visibility 3 statute miles...thunderstorm with moderate rain showers...clouds broken at 3,000 feet with cumulonimbus clouds...from 0400Z...winds from 140° at 8 knots...visibility greater than 6 miles...clouds at 4,000 scattered and overcast at 8,000...temporarily between 0400Z and 0800Z...visibility 3 miles...thunderstorms with moderate rain showers...clouds overcast at 3,000 feet with cumulonimbus clouds...becoming between 0800Z and 1000Z...wind from 320° at 7 knots...end of report (=).

AREA FORECASTS (FA)
The aviation area forecast (FA) gives a picture of clouds, general weather conditions, and visual meteorological conditions (VMC) expected over a large area encompassing several states. There are six areas for which area forecasts are published in the contiguous 48 states. Area forecasts are issued three times a day and are valid for 18 hours. This type of forecast gives information vital to en route operations as well as forecast information for smaller airports that do not have terminal forecasts.

Area forecasts are typically disseminated in four sections and include the following information:

1. Header—This gives the location identifier of the source of the FA, the date and time of issuance, the valid forecast time, and the area of coverage.

Example:
DFWC FA 120945
SYNOPSIS AND VFR CLDS/WX
SYNOPSIS VALID UNTIL 130400
CLDS/WX VALID UNTIL 122200…OTLK VALID
122200-130400
OK TX AR LA MS AL AND CSTL WTRS

Explanation:
The area forecast shows information given by Dallas Fort Worth, for the region of Oklahoma, Texas, Arkansas, Louisiana, Mississippi, and Alabama, as well as a portion of the gulf coastal waters. It was issued on the 12th day of the month at 0945. The synopsis is valid from the time of issuance until 0400 hours on the 13th. VFR clouds and weather information on this area forecast is valid until 2200 hours on the 12th and the outlook is valid until 0400 hours on the 13th.

2. Precautionary Statements—IFR conditions, mountain obscurations, and thunderstorm hazards are described in this section. Statements made here regarding height are given in MSL, and if given otherwise, AGL or CIG (ceiling) will be noted.

Example:
SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN.
TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND IFR CONDS.
NON MSL HGTS DENOTED BYAGL OR CIG.

Explanation:
The area forecast covers VFR clouds and weather, so the precautionary statement warns that AIRMET Sierra should be referenced for IFR conditions and mountain obscuration. The code TS indicates the possibility of thunderstorms and implies there may be an occurrence of severe or greater turbulence, severe icing, low-level wind shear, and IFR conditions. The final line of the precautionary statement alerts the user that heights, for the most part, are mean sea level (MSL). Those that are not MSL will be above ground level (AGL) or ceiling (CIG).

3. Synopsis—The synopsis gives a brief summary identifying the location and movement of pressure systems, fronts, and circulation patterns.

Example:
SYNOPSIS…LOW PRES TROF 10Z OK/TX PNHDL
AREA FCST MOV EWD INTO CNTRL-SWRN OK
BY 04Z. WRMFNT 10Z CNTRL OK-SRN AR-NRN
MS FCST LIFT NWD INTO NERN OK-NRN AR
EXTRM NRN MS BY 04Z.

Explanation:
As of 1000 Zulu, there is a low pressure trough over the Oklahoma and Texas panhandle area, which is forecast to move eastward into central southwestern Oklahoma by 0400 Zulu. A warm front located over central Oklahoma, southern Arkansas, and northern Mississippi at 1000 Zulu is forecast to lift northwestward into northeastern Oklahoma, northern Arkansas, and extreme northern Mississippi by 0400 Zulu.

4. VFR Clouds and Weather—This section lists expected sky conditions, visibility, and weather for the next 12 hours and an outlook for the following 6 hours.

Example:
S CNTRL AND SERN TX
AGL SCT-BKN010. TOPS 030. VIS 3-5SM BR.
14-16Z BECMG AGL SCT030. 19Z AGL SCT050.
OTLK…VFR
OK
PNDLAND NW…AGL SCT030 SCT-BKN100.
TOPS FL200.
15Z AGL SCT040 SCT100. AFT 20Z SCT TSRA
DVLPG..FEW POSS SEV. CB TOPS FL450.
OTLK…VFR

Explanation:
In south central and southeastern Texas, there is a scattered to broken layer of clouds from 1,000 feet AGL with tops at 3,000 feet, visibility is 3 to 5 statute miles in mist. Between 1400 Zulu and 1600 Zulu, the cloud bases are expected to increase to 3,000 feet AGL.
After 1900 Zulu, the cloud bases are expected to continue to increase to 5,000 feet AGL and the outlook is VFR.
In northwestern Oklahoma and panhandle, the clouds are scattered at 3,000 feet with another scattered to broken layer at 10,000 feet AGL, with the tops at 20,000 feet. At 1500 Zulu, the lowest cloud base is expected to increase to 4,000 feet AGL with a scattered layer at 10,000 feet AGL. After 2000 Zulu, the forecast calls for scattered thunderstorms with rain developing and a few becoming severe; the cumulonimbus clouds will have tops at flight level 450 or 45,000 feet MSL.
It should be noted that when information is given in the area forecast, locations may be given by states, regions, or specific geological features such as mountain ranges. Figure 11-6 shows an area-forecast chart with six regions of forecast, states, regional areas, and common geographical features.

IN-FLIGHT WEATHER ADVISORIES
In-flight weather advisories, which are provided to en route aircraft, are forecasts that detail potentially hazardous weather. These advisories are also available to pilots prior to departure for flight planning purposes.

An in-flight weather advisory is issued in the form of either an AIRMET, SIGMET, or Convective SIGMET.

AIRMAN'S METEOROLOGICAL INFORMATION (AIRMET)
AIRMETs (WAs) are examples of in-flight weather advisories that are issued every 6 hours with intermediate updates issued as needed for a particular area forecast region. The information contained in an AIRMET is of operational interest to all aircraft, but the weather section concerns phenomena considered potentially hazardous to light aircraft and aircraft with limited operational capabilities.

An AIRMET includes forecast of moderate icing, moderate turbulence, sustained surface winds of 30 knots or greater, widespread areas of ceilings less than 1,000 feet and/or visibilities less than 3 miles, and extensive mountain obscurement.

Each AIRMET bulletin has a fixed alphanumeric designator, numbered sequentially for easy identification, beginning with the first issuance of the day. SIERRA is the AIRMET code used to denote instrument flight rules (IFR) and mountain obscuration; TANGO is used to denote turbulence, strong surface winds, and low-level wind shear; and ZULU is used to denote icing and freezing levels.

Example:
DFWTWA 241650
AIRMET TANGO UPDT 3 FOR TURBC… STG
SFC WINDS AND LLWS VALID UNTIL 242000
AIRMET TURBC… OK TX…UPDT
FROM OKC TO DFW TO SAT TO MAF TO CDS
TO OKC OCNL MDT TURBC BLO 60 DUE TO
STG AND GUSTY LOW LVL WINDS. CONDS
CONTG BYD 2000Z

Explanation:
This AIRMET was issued by Dallas Fort Worth on the 24th day of the month, at 1650 Zulu time. On this third update, the AIRMET Tango is issued for turbulence, strong surface winds, and low-level wind shear until 2000 Zulu on the same day. The turbulence section of the AIRMET is an update for Oklahoma and Texas. It defines an area from Oklahoma City to Dallas, Texas, to San Antonio, to Midland, Texas, to Childress, Texas, to Oklahoma City that will experience occasional moderate turbulence below 6,000 feet due to strong and gusty low-level winds. It also notes that these conditions are forecast to continue beyond 2000 Zulu.

SIGNIFICANT METEOROLOGICAL INFORMATION (SIGMET)
SIGMETs (WSs) are in-flight advisories concerning non-convective weather that is potentially hazardous to all aircraft. They report weather forecasts that include severe icing not associated with thunderstorms, severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms, dust storms or sandstorms that lower surface or in-flight visibilities to below 3 miles, and volcanic ash.

SIGMETs are unscheduled forecasts that are valid for 4 hours, but if the SIGMET relates to hurricanes, it is valid for 6 hours.

A SIGMET is issued under an alphabetic identifier, from November through Yankee, excluding Sierra and Tango. The first issuance of a SIGMET is designated as a UWS, or Urgent Weather SIGMET. Re-issued SIGMETs for the same weather phenomenon are sequentially numbered until the weather phenomenon ends.

Example:
SFOR WS 100130
SIGMET ROME02 VALID UNTIL 100530
OR WA
FROM SEA TO PDT TO EUG TO SEA
OCNL MOGR CAT BTN 280 AND 350 EXPCD
DUE TO JTSTR.
CONDS BGNG AFT 0200Z CONTG BYD 0530Z .

Explanation:
This is SIGMET Romeo 2, the second issuance for this weather phenomenon. It is valid until the 10th day of the month at 0530 Zulu time. This SIGMET is for Oregon and Washington, for a defined area from Seattle to Portland to Eugene to Seattle. It calls for occasional moderate or greater clear air turbulence between 28,000 and 35,000 feet due to the location of the jetstream. These conditions will be beginning after 0200 Zulu and will continue beyond the forecast scope of this SIGMET of 0530 Zulu.

CONVECTIVE SIGNIFICANT METEOROLOGICAL INFORMATION (WST)
A Convective SIGMET (WST) is an in-flight weather advisory issued for hazardous convective weather that affects the safety of every flight. Convective SIGMETs are issued for severe thunderstorms with surface winds greater than 50 knots, hail at the surface greater than or equal to 3/4 inch in diameter, or tornadoes.

They are also issued to advise pilots of embedded thunderstorms, lines of thunderstorms, or thunderstorms with heavy or greater precipitation that affect 40 percent or more of a 3,000 square foot or greater region.

Convective SIGMETs are issued for each area of the contiguous 48 states but not Alaska or Hawaii.

Convective SIGMETs are issued for the eastern (E), western (W), and central (C) United States. Each report is issued at 55 minutes past the hour, but special reports can be issued during the interim for any reason. Each forecast is valid for 2 hours. They are numbered sequentially each day from 1-99, beginning at 00 Zulu time. If no hazardous weather exists, the Convective SIGMET will still be issued; however, it will state "CONVECTIVE SIGMET…. NONE."

Example:
MKCC WST 221855
CONVECTIVE SIGMET 21C
VALID UNTIL 2055
KS OK TX
VCNTY GLD-CDS LINE
NO SGFNT TSTMS RPRTD
LINE TSTMS DVLPG BY 1955Z WILL MOV EWD
30-35 KT THRU 2055Z
HAIL TO 2 IN PSBL

Explanation:
This Convective SIGMET provides the following information: The WST indicates this report is a Convective SIGMET. The current date is the 22nd of the month and it was issued at 1855 Zulu. It is Convective SIGMET number 21C, indicating that it is the 21st consecutive report issued for the central United States. This report is valid for 2 hours until 2055 Zulu time. The Convective SIGMET is for an area from Kansas to Oklahoma to Texas, in the vicinity of a line from Goodland, Kansas, to Childress, Texas. No significant thunderstorms are being reported, but a line of thunderstorms will develop by 1955 Zulu time and will move eastward at a rate of 30-35 knots through 2055 Zulu. Hail up to 2 inches in size is possible with the developing thunderstorms.

WINDS AND TEMPERATURE ALOFT FORECAST (FD)
Winds and temperatures aloft forecasts provide wind and temperature forecasts for specific locations in the contiguous United States, including network locations in Hawaii and Alaska. The forecasts are made twice a day based on the radiosonde upper air observations taken at 0000Z and 1200Z.

Through 12,000 feet are true altitudes and above 18,000 feet are pressure altitudes. Wind direction is always in reference to true north and windspeed is given in knots. The temperature is given in degrees Celsius. No winds are forecast when a given level is within 1,500 feet of the station elevation. Similarly, temperatures are not forecast for any station within 2,500 feet of the station elevation.

If the windspeed is forecast to be greater than 100 knots but less than 199 knots, the computer adds 50 to the direction and subtracts 100 from the speed. To decode this type of data group, the reverse must be accomplished. For example, when the data appears as "731960," subtract 50 from the 73 and add 100 to the 19, and the wind would be 230° at 119 knots with a temperature of –60°C. If the windspeed is forecast to be 200 knots or greater, the wind group is coded as 99 knots. For example, when the data appears as "7799," subtract 50 from 77 and add 100 to 99, and the wind is 270° at 199 knots or greater. When the forecast windspeed is calm or less than 5 knots, the data group is coded "9900," which means light and variable.

Forecast Table

FD KWBC 151640 BASED ON 151200Z DATA VALID 151800Z FOR USE 1700-2100Z TEMPS NEGATIVE ABV 24000
FD AMA DEN	3000	6000 2714	9000 2725+00 2321-04	12000 2625-04 2532-08	18000 2531-15 2434-19	24000 2542-27 2441-31	30000 265842 235347

Explanation of Forecast Table:
The heading indicates that this FD was transmitted on the 15th of the month at 1640Z and is based on the 1200 Zulu radiosonde. The valid time is 1800 Zulu on the same day and should be used for the period between 1700Z and 2100Z. The heading also indicates that the temperatures above 24,000 feet MSL are negative.

Since the temperatures above 24,000 feet are negative, the minus sign is omitted.

A 4-digit data group shows the wind direction in reference to true north, and the windspeed in knots. The elevation at Amarillo, TX (AMA) is 3,605 feet, so the lowest reportable altitude is 6,000 feet for the forecast winds. In this case, "2714" means the wind is forecast to be from 270° at a speed of 14 knots.

A 6-digit group includes the forecast temperature aloft.

The elevation at Denver (DEN) is 5,431 feet, so the lowest reportable altitude is 9,000 feet for the winds and temperature forecast. In this case, "2321-04" indicates the wind is forecast to be from 230° at a speed of 21 knots with a temperature of –4°C.

AVIATION WEATHER REPORTS

Aviation weather reports are designed to give accurate depictions of current weather conditions. Each report provides current information that is updated at different times. Some typical reports are aviation routine weather reports (METAR), pilot weather reports (PIREPs), and radar weather reports (SDs).

AVIATION ROUTINE WEATHER REPORT (METAR)
An aviation routine weather report, or METAR, is an observation of current surface weather reported in a standard international format. While the METAR code has been adopted worldwide, each country is allowed to make modifications to the code. Normally, these differences are minor but necessary to accommodate local procedures or particular units of measure. This discussion of METAR will cover elements used in the United States.

Example:
METAR KGGG 161753Z AUTO 14021G26 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

A typical METAR report contains the following information in sequential order:

1. Type of Report—There are two types of METAR reports. The first is the routine METAR report that is transmitted every hour. The second is the aviation selected special weather report (SPECI). This is a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information.
2. Station Identifier—Each station is identified by a four-letter code as established by the International Civil Aviation Organization (ICAO). In the 48 contiguous states, the letter "K" precedes a unique three-letter identifier. For example, the letters "KGGG," K being the country designation and GGG being the airport identifier, identifies Gregg County Airport in Longview, Texas. In other regions of the world, including Alaska and Hawaii, the first two letters of the four-letter ICAO identifier indicate the region, country, or state. Alaska identifiers always begin with the letters "PA" and Hawaii identifiers always begin with the letters "PH". A list of station identifiers can be found at an FSS or NWS office.
3. Date and Time of Report—The date and time (161753Z) are depicted in a six-digit group. The first two digits of the six-digit group are the date. The last four digits are the time of the METAR, which is always given in Coordinated Universal Time (UTC). A "Z" is appended to the end of the time to denote the time is given in Zulu time (UTC) as opposed to local time.
4. Modifier—Modifiers denote that the METAR came from an automated source or that the report was corrected. If the notation "AUTO" is listed in the METAR, the report came from an automated source. It also lists "AO1" or "AO2" in the remark section to indicate the type of precipitation sensors employed at the automated station. When the modifier "COR" is used, it identifies a corrected report sent out to replace an earlier report that contained an error. Example:METAR KGGG 161753Z COR
5. Wind—Winds are reported with five digits (14021) unless the speed is greater than 99 knots, in which case the wind is reported with six digits. The first three digits indicate the direction the wind is blowing in tens of degrees. If the wind is variable, it is reported as "VRB". The last two digits indicate the speed of the wind in knots (KT) unless the wind is greater than 99 knots, in which case it is indicated by three digits. If the winds are gusting, the letter "G" follows the windspeed (G26). After the letter "G", the peak gust recorded is provided. If the wind varies more than 60° and the windspeed is greater than 6 knots, a separate group of numbers, separated by a "V", will indicate the extremes of the wind directions.
6. Visibility—The prevailing visibility (3/4 SM) is reported in statute miles as denoted by the letters "SM". It is reported in both miles and fractions of miles. At times, RVR, or runway visual range is reported following the prevailing visibility. RVR is the distance a pilot can see down the runway in a moving aircraft. When RVR is reported, it is shown with an R, then the runway number followed by a slant, then the visual range in feet. For example, when the RVR is reported as R17L/1400FT, it translates to a visual range of 1,400 feet on runway 17 left.
7. Weather—Weather can be broken down into two different categories: qualifiers and weather phenomenon (+TSRA BR). First, the qualifiers of intensity, proximity, and the descriptor of the weather will be given. The intensity may be light (-), moderate ( ), or heavy (+). Proximity only depicts weather phenomena that are in the airport vicinity. The notation "VC" indicates a specific weather phenomenon is in the vicinity of 5 to 10 miles from the airport. Descriptors are used to describe certain types of precipitation and obscurations. Weather phenomena may be reported as being precipitation, obscurations, and other phenomena such as squalls or funnel clouds. Descriptions of weather phenomena as they begin or end, and hailstone size are also listed in the remarks sections of the report.
8. Sky Condition—Sky condition (BKN008 OVC012CB) is always reported in the sequence of amount, height, and type or indefinite ceiling/height (vertical visibility). The heights of the cloud bases are reported with a three-digit number in hundreds of feet above the ground. Clouds above 12,000 feet are not detected or reported by an automated station. The types of clouds, specifically towering cumulus (TCU) or cumulonimbus (CB) clouds are reported with their height. Contractions are used to describe the amount of cloud coverage and obscuring phenomena. The amount of sky coverage is reported in eighths of the sky from horizon to horizon.
9. Temperature and Dewpoint—The air temperature and dewpoint are always given in degrees Celsius (18/17). Temperatures below 0°C are preceded by the letter "M" to indicate minus.
10. Altimeter Setting—The altimeter setting is reported as inches of mercury in a four-digit number group (A2970). It is always preceded by the letter "A". Rising or falling pressure may also be denoted in the remarks sections as "PRESRR" or "PRESFR" respectively.
11. Remarks—Comments may or may not appear in this section of the METAR. The information contained in this section may include wind data, variable visibility, beginning and ending times of particular phenomenon, pressure information, and various other information deemed necessary. An example of a remark regarding weather phenomenon that does not fit in any other category would be: OCNL LTGICCG. This translates as occasional lightning in the clouds, and from cloud to ground. Automated stations also use the remarks section to indicate the equipment needs maintenance. The remarks section always begins with the letters "RMK".

Example:
METAR BTR 161753Z 14021G26 3/4SM -RA BR BKN008 OVC012 18/17 A2970 RMK PRESFR

Explanation:
Type of Report: ...............Routine METAR
Location: ........................Baton Rouge, Louisiana
Date: ...............................16th day of the month
Time: ..............................1753 Zulu
Modifier: ........................None shown
Wind Information: ..........Winds 140° at 21 knots gusting to 26 knots
Visibility: ........................3/4 statute mile
Weather: .........................light rain and mist
Sky Conditions: ..............Skies broken 800 feet, overcast 1,200
Temperature: ..................Temperature 18°C, dewpoint 17°C
Altimeter: .......................29.70 in. Hg.
Remarks: ........................Barometric pressure is falling.

PILOT WEATHER REPORTS (PIREPs)
Pilot weather reports provide valuable information regarding the conditions as they actually exist in the air, which cannot be gathered from any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear and turbulence, and the location of in-flight icing. If the ceiling is below 5,000 feet, or visibility is at or below 5 miles, ATC facilities are required to solicit PIREPs from pilots in the area.

When unexpected weather conditions are encountered, pilots are encouraged to make a report to an FSS or ATC. When a pilot weather report is filed, the ATC facility or FSS will add it to the distribution system to brief other pilots and provide in-flight advisories.

PIREPs are easy to file and a standard reporting form outlines the manner in which they should be filed. PIREPs are normally transmitted as an individual report, but may be appended to a surface report. Pilot reports are easily decoded and most contractions used in the reports are self-explanatory.

Example:
UA/OV GGG 090025/ M 1450/ FL 060/ TP C182/ SK 080 OVC/ WX FV 04R/ TA 05/ WV 270030/ TB LGT/ RM HVY RAIN

Explanation:
Type: ...............................Routine pilot report
Location: ........................25 NM out on the 090° radial, Gregg County VOR
Time: ..............................1450 Zulu Altitude or Flight Level: 6,000 feet
Aircraft Type: .................Cessna 182
Sky Cover: ......................8,000 overcast
Visibility/Weather: ..........4 miles in rain
Temperature: ..................5° Celsius
Wind: ..............................270° at 30 knots
Turbulence: ....................Light
Icing: ..............................None reported
Remarks: ........................Rain is heavy.

RADAR WEATHER REPORTS (SD)
Areas of precipitation and thunderstorms are observed by radar on a routine basis. Radar weather reports are issued by radar stations at 35 minutes past the hour, with special reports issued as needed.

Radar weather reports provide information on the type, intensity, and location of the echo top of the precipitation. These reports may also include direction and speed of the area of precipitation as well as the height and base of the precipitation in hundreds of feet MSL. RAREPs are especially valuable for preflight planning to help avoid areas of severe weather. However, radar only detects objects in the atmosphere that are large enough to be considered precipitation. Cloud bases and tops, ceilings, and visibility are not detected by radar.

A typical RAREP will include:

• Location identifier and time of radar observation.
• Echo pattern:

1. Line (LN)—A line of precipitation echoes at least 30 miles long, at least four times as long as it is wide, and at least 25 percent coverage within the line.
2. Area (AREA)—A group of echoes of similar type and not classified as a line.
3. Single Cell (CELL)—A single isolated convective echo such as a rain shower.

• Area coverage in tenths.
• Type and intensity of weather.
• Azimuth, referenced to true north, and range, in nautical miles, from the radar site, of points defining the echo pattern. For lines and areas, there will be two azimuth and range sets that define the pattern. For cells, there will be only one azimuth and range set.
• Dimension of echo pattern—The dimension of an echo pattern is given when the azimuth and range define only the centerline of the pattern.
• Cell movement—Movement is only coded for cells; it will not be coded for lines or areas.
• Maximum top of precipitation and location. Maximum tops may be coded with the symbols
• "MT" or "MTS." If it is coded with "MTS," it means that satellite data as well as radar information was used to measure the top of the precipitation.
• If the word "AUTO" appears in the report, it means the report is automated from WSR-88D weather radar data.
• The last section is primarily used to prepare radar summary charts, but can be used during preflight to determine the maximum precipitation intensity within a specific grid box. The higher the number, the greater the intensity. Two or more numbers appearing after a grid box reference, such as PM34, indicates precipitation in consecutive grid boxes.

Example:
TLX 1935 LN 8 TRW++ 86/40 199/115 20W C2425 MTS 570 AT 159/65 AUTO ^MO1 NO2 ON3 PM34 QM3 RL2=

Explanation:
The radar report gives the following information: The report is automated from Oklahoma City and was made at 1935 UTC. The echo pattern for this radar report indicates a line of echoes covering 8/10ths of the area. Thunderstorms and very heavy rain showers are indicated. The next set of numbers indicates the azimuth that defines the echo (86° at 40 NM and 199° at 115 NM). Next, the dimension of this echo is given as 20 nautical miles wide (10 nautical miles on either side of the line defined by the azimuth and range). The cells within the line are moving from 240° at 25 knots. The maximum top of the precipitation, as determined by radar and satellite, is 57,000 feet and it is located on the 159° radial, 65 NM out. The last line indicates the intensity of the precipitation, for example in grid QM the intensity is 3 or heavy precipitation. (1 is light and 6 is extreme.)